1. Field of the Invention
The present invention relates to an air conditioning system and a control method thereof, and more particularly, to an air conditioning system and a control method thereof, which is improved in a heating effect while performing a heating operation under a condition in which an outdoor temperature is low.
2. Description of the Related Art
An air conditioning system employs a refrigerating cycle to condition state quantity such as room temperature and humidity of a residential building or an official building. That is, the air conditioning system repeats compression, condensation, expansion and evaporation of refrigerant, so that heating is achieved by heat radiation due to the condensation in winter, and cooling is achieved by heat absorption due to the evaporation.
One type of air conditioning system is a gas engine-driven heat pump (GHP) type air conditioning system, which uses driving force of a gas engine to drive a compressor, and recovers waste heat of the gas engine. The GHP type air conditioning system substitutes for an electric motor-driven heat pump (EHP) type air conditioning system. In the EHP type air conditioning system, there exists a problem of a disequilibrium between demand and supply of electric power according to a cooling demand increase in summer.
A conventional air conditioning system has the following problems while performing a heating operation under the condition that outdoor temperature is low.
First, when heating is performed at a low outdoor temperature, pressure of the refrigerant discharged from the compressor (i.e., a high pressure part) and pressure of the refrigerant introduced into the compressor (i.e., a low pressure part) are all low even though the gas engine is rotated at a maximum speed. This means that an amount of the circulated refrigerant is small, which causes a heating effect of the air conditioning system to be lowered.
Second, in the conventional air conditioning system, the heating effect depends on adjustment of an outdoor expansion valve. Therefore, the heating effect has a limit when the outdoor temperature is low. In the case of the GHP type air conditioning system, the heating effect may be adjusted by controlling a cooling water valve to adjust cooling water heated by waste heat of the gas engine. The allowable adjustment is limited.